crypto: avoid unitializing ECDH objects on error

The previous code changed the private key of the ECDH object, but
removed the public key if deriving it from the private key failed.
Instead, if deriving the public key fails, neither the private nor
the public key stored in the ECDH object should be updated.

src/node_crypto.cc

@@ -5710,21 +5710,20 @@ void ECDH::SetPrivateKey(const FunctionCallbackInfo<Value>& args) {
     return env->ThrowError("Private key is not valid for specified curve.");
   }
 
-  int result = EC_KEY_set_private_key(ecdh->key_.get(), priv.get());
+  ECKeyPointer new_key(EC_KEY_dup(ecdh->key_.get()));
+  CHECK(new_key);
+
+  int result = EC_KEY_set_private_key(new_key.get(), priv.get());
   priv.reset();
 
   if (!result) {
     return env->ThrowError("Failed to convert BN to a private key");
   }
 
-  // To avoid inconsistency, clear the current public key in-case computing
-  // the new one fails for some reason.
-  EC_KEY_set_public_key(ecdh->key_.get(), nullptr);
-
   MarkPopErrorOnReturn mark_pop_error_on_return;
   USE(&mark_pop_error_on_return);
 
-  const BIGNUM* priv_key = EC_KEY_get0_private_key(ecdh->key_.get());
+  const BIGNUM* priv_key = EC_KEY_get0_private_key(new_key.get());
   CHECK_NOT_NULL(priv_key);
 
   ECPointPointer pub(EC_POINT_new(ecdh->group_));
@@ -5735,8 +5734,11 @@ void ECDH::SetPrivateKey(const FunctionCallbackInfo<Value>& args) {
     return env->ThrowError("Failed to generate ECDH public key");
   }
 
-  if (!EC_KEY_set_public_key(ecdh->key_.get(), pub.get()))
+  if (!EC_KEY_set_public_key(new_key.get(), pub.get()))
     return env->ThrowError("Failed to set generated public key");
+
+  EC_KEY_copy(ecdh->key_.get(), new_key.get());
+  ecdh->group_ = EC_KEY_get0_group(ecdh->key_.get());
 }